Limiting message diffusion between mobile devices

ABSTRACT

Information with local relevance is diffused locally using mobile devices equipped with non-wired short-range communication means, the information being propagated from an originating point in messages passed from device to device in an unstructured way. The devices implement measures for limiting message propagation. For a device that is arranged to propagate a received message multiple times, these measures include increasing (75) the interval between retransmissions in dependence on how many times the same message has been received by the device either in total or during a recent period.

FIELD OF THE INVENTION

[0001] The present invention relates to the local diffusion ofinformation, particularly information of local relevance, using mobiledevices; in particular, the present invention concerns limiting unduediffusion of messages containing the information

BACKGROUND OF THE INVENTION

[0002] Mobile devices with communications capability are becomingubiquitous, the most common being the cell phone and other devicesemploying cellular radio technology. Many services are being implementedusing such devices and many more may be expected as informationregarding the location or position of the mobile device becomes readilyavailable through the implementation of location discovery within themobile radio infrastructure.

[0003] One type of service that is emerging is the distribution of localinformation which is relevant only to a particular narrow geographiclocation and need only be communicated to people within that location.Such information is usually distributed as a result of a requestgenerated from a mobile device, the request either including thedevice's location or authorizing the obtaining of the device's locationfrom a location server of the mobile radio infrastructure. Thelocally-relevant information can also be pushed over the mobile radioinfrastructure to mobile devices within a given locality, though thecosts of doing so are high. The type of information which it is mostdesirable to be able to push is information with a certain immediacy toit either because the information will go out of date quickly or becausethe target audience is transitory. One example is where a theatre stillhas seats available for a show shortly starting, and would like to offerthe seats at half price. Another example is information about consumergoods (particularly new products or products under special promotion)which a shop wishes to advertise to consumers passing by.

[0004] In view of the cost and complexity of using mobile radio networksto push information, it would be useful to have a different way ofdistributing local information which has immediacy to it.

[0005] It may also be noted that although, as indicted above, locationinformation will become increasingly available, this will only be tousers of certain types of devices (cellular radio devices, GPS-equippeddevices). Other devices will not have the appropriate capability todirectly access location information and will therefore not be able tobenefit from the full range of location-based services. Even if a devicedoes have access to location discovery technology, the level of accuracymay deteriorate in the prevailing conditions (receivability of basestations and satellites, interference from buildings etc.) reducing theeffectiveness of location based services. In both the foregoing cases itwould be desirable for accurate location information to be locallydistributed (but only over a short distance so as not to unacceptablyaffect its accuracy).

[0006] A number of technologies exist for the short range communicationof information between mobile devices. These technologies includeinfra-red based technologies and low-power radio technologies(including, in particular, the recent “Bluetooth” short range wirelessstandard). Depending on the technology implementation, differing typesof message propagation will be enabled including asynchronous messagebroadcast, and multicast and point-to-point duplex connectionsestablished after coordination and negotiation between communicatingdevices.

[0007] Temporary networks using collections of mobile devices are ofcurrent interest. In particular, the Ad Hoc Networks Working Group ofthe IETF (Internet Engineering Task Force) is looking at the situationwhere two devices can temporarily communicate for a short time, viaintermediate mobile devices; in this case, there is assumed to be somesort of temporary connectivity between the two devices across ashort-lived mobile network. This work is primarily aimed at scenariossuch as people in a conference environment sending mail to one anothervia intermediate devices, a situation which is dynamic, but which willtend to be temporarily static. Another example of an Ad Hoc network isthe connection of ships or tanks in a military situation, where thetopology of the network is evolving, but gradually over a period oftime.

[0008] It is an object of the present invention to facilitate the localdiffusion of information.

SUMMARY OF THE INVENTION

[0009] According to the present invention, there is provided a method oflocally diffusing information for presentation to users of mobiledevices, the method involving propagating the information from anoriginating point in messages passed from device to device by non-wiredshort-range communication means of the devices, the number of copies ofa message in propagation initially tending to increase due to thepropagation activities of the receiving devices and then dying away asthe devices implement propagation limitation measures for the message,at least one device being operative to send messages multiple times withthe interval between retransmissions of the message being dependent onhow many times the same message has been received by the device eitherin total or during a recent period.

[0010] As used herein, the phrase “number of copies of a message inpropagation” includes both message copies in transit and message copiesresiding in a device that are still considered active for onwardpropagation.

[0011] According to another aspect of the present invention, there isprovided a mobile device for locally diffusing information to otherdevices for presentation to their users, the mobile device comprising:

[0012] a message store;

[0013] a short-range wireless transceiver for receiving messages andstoring them to said store, and for transmitting messages retrieved fromthe store;

[0014] a message receive/transmit counter for recording how many timeseach message is received and transmitted; and

[0015] a message-propagation controller operative to cause messages heldin said store to be transmitted multiple times with the interval betweenretransmissions of each message being dependent on how many times thesame message has been received by the device, either in total or duringa recent period, as indicated by said counter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] A method and mobile device, both embodying the present invention,for locally diffusing information will now be described, by way ofnon-limiting example, with reference to the accompanying diagrammaticdrawings, in which:

[0017]FIG. 1 is a diagram illustrating the propagation of aninformation-bearing message in accordance with the information-diffusionmethod embodying the invention;

[0018]FIG. 2 is a diagram showing the format of the information-bearingmessage being propagated in FIG. 1;

[0019]FIG. 3 is a diagram of a mobile device involved in messagepropagation in FIG. 1;

[0020]FIG. 4 is a diagram depicting the operations carried out by theFIG. 3 device upon first receipt of a message;

[0021]FIG. 5 is a diagram depicting the operations carried out by theFIG. 3 device upon timeout of a sending interval;

[0022]FIG. 6 is a diagram depicting the operations carried out by theFIG. 3 device for removing old, unwanted, messages from a message storeof the device;

[0023]FIG. 7A is a diagram illustrating the variation of live messagedensity around two originating points; and

[0024]FIG. 7B is a diagram illustrating the percentage of messageslikely to be received from one of the FIG. 7A originating points by adevice moving past that point.

BEST MODE FOR CARRYING OUT THE INVENTION

[0025]FIG. 1 illustrates the general operation of an embodiment of theinvention. This embodiment involves a plurality of mobile devices 10each equipped with the same type of non-wired short-range communicationmeans, such as an IR or Bluetooth radio system. The mobile devices areindividually labelled A to E and may be carried by pedestrians and/orcycles, vehicles or other means of transport. Also shown in FIG. 2 is anoriginating point (source) 12, and a static relay station 13, both ofwhich are equipped with the same type of short range communication meansas the mobile devices 10. The actual form of the short-rangecommunications technology employed by the devices 10, originating point12, and relay station 13, is not critical to the present invention andany suitable technology can be used together with any appropriatepropagation regime (broadcast, multicast, repeated one-to-one, etc.).

[0026] In operation, originating point 12 sends out information intendedfor the users of the mobile devices, by including the information in amessage which it then transmits one or more times via its short-rangecommunications means. The message is picked up by an adjacent device andthen propagated on to other devices thereby diffusing the informationover the community of devices 10 for presentation to the users.

[0027] More particularly, in the illustrated example, device A picks upthe message transmitted by originating source 12 and propagates it on todevice B using the short-range communications means of the two devices.Device B then moves position before propagating on the message to deviceC. Device C now also moves before propagating the message both to deviceD and to the fixed relay station 13. At around the same time asreceiving the message from device C, device D receives the message fromdevice A, the latter having moved from its starting position. Device Dthen moves position and receives the message again, this time from adevice E that received the message from the relay station 13. Althoughdevice D has ended up receiving the message three times, this is not aproblem since the message carries a message ID that is present in allcopies of the same message, thereby enabling a recipient device (here,device D) to recognise that it has received multiple copies of the samemessage.

[0028] As can be seen, in the illustrated example, message diffusion is,in part, due to the movement of the devices since although the actualtransfer of a message from one device to another is due to transmissionusing the short-range communications means, devices may only be broughtinto range as a result of the movement of one or other of the devices.

[0029] The propagation of the message from device to device is effectedin an unstructured way in the sense that the messages are not routed inany particular way and there is no target final destination specified;instead, the message diffusion relies on the involvement of whateverdevices are conveniently available and enabled to participate in theprocess.

[0030] The originating point need not be fixed in position, being, forexample, a mobile device similar to devices 10. Furthermore, messagediffusion does not require the involvement of a relay station 13 thoughsuch stations may be useful in extending the range of message diffusion.

[0031] The device inter-connectivity required by the above process needonly be of a highly transitory nature, it not even being necessary forthe devices to connect long enough for the message-receiving device tosend a reply (in other words, unacknowledged message transfer isoperationally adequate). This characteristic enables moving devices tobe more easily utilised before they are out of range. This highlytransient nature of device inter-connectivity contrasts with the type ofnetwork being considered by the Ad Hoc Networks Working Group of theIETF (see above), where the objective is primarily to establish, albeittemporarily, a temporary connection between endpoints.

[0032] With respect to the type of information included in a message,this will generally be locality information, that is:

[0033] information with at least an item that is explicitly orimplicitly of local relevance, such as commercial advertising andpromotional information relevant to a local retail outlet (theinformation may even include an electronic voucher that the user of arecipient device can present to the retail outlet to receive a discountor other reward)

[0034] in such cases the originating point will generally be at oradjacent the retail outlet concerned; and/or

[0035] the position of the originating point (whereby to enable devicesnot equipped with location discovery means to ascertain their locationindirectly, this position information then being provided, for example,to a location-aware service using the short-range communications meansof the device or, possibly, a cellular radio capability possessed by thedevice. Position may be specified in any appropriate way such aslongitude and latitude, local grid coordinates, names of local places,etc.

[0036] The information need not be restricted to visually displayableinformation and can take the form of short audio advertisements or lowbit-rate music clips to consumers within a particular vicinity, forexample to advertise products within a record/CD/music kiosk type ofshop within a shopping mall.

Restriction Mechanisms

[0037] In order to ensure that all devices in the area around anoriginating point have the opportunity of receiving a message,propagating devices are preferably configured to seek to multiply thenumber of message copies in circulation, either by sending a messagemultiple times and/or by sending the message to multiple other devices.For example, a device can be configured to send on a message immediatelyit is received and then at timed intervals thereafter, and/or upondetecting another device close by. In this way, an initial build up ofthe number of active message copies can be achieved provided there aresufficient devices in the area.

[0038] However, the unrestricted propagation of messages is generallyundesirable as it can result in information continuing to circulateafter it has become out-of-date, and being propagated into areas whereit is not relevant; also, device and bandwidth resources will beunnecessarily consumed. What is required is that after an initial buildup of the number of active message copies, this number should die away.To achieve this, several different restriction mechanisms are preferablyemployed in the mobile devices 10. Suitable restriction mechanisms aredescribed below and particular implementations are then given withreference to the FIG. 3 embodiment of mobile device 10. The restrictionmechanisms can be employed individually or selected combinations inorder to achieve desired restriction characteristics.

[0039] Message life control mechanisms—the life of a message can berestricted in a number of ways, for example by using:

[0040] a time-to-live limit set on a message as sent from theoriginating point;

[0041] a hop limit set on the number of times the message from theoriginating point can be propagated along a chain of propagation;

[0042] a locale limit outside of which the information should not to bepropagated.

[0043] These limits generally involve the inclusion of propagationlimitation data in each propagated message copy, with each receivingdevice examining this data to determine whether it should treat themessage as no longer alive (that is, no longer one which should beconsidered for propagation).

[0044] With respect to the time-to-live limit, this can be implementedby specifying a time value (such as 10 minutes) in the message as sentby the originating point. At each device the message transits, this timevalue set in the message is decreased by an amount corresponding to thetime the message has been held in the device. A receiving device canthen determine whether a received message has exceeded its initiallifetime by examining the time value in the message and determiningwhether the message has been held for longer than that time—if it has,the message is treated as no longer alive or active (that is, dead) andis therefore not propagated further. This way of determining lifespanhas the advantage that the clocks of the different devices do not needto be in sync with each other (if, in fact, this could be guaranteed,then, of course, it would only be necessary for the originating point tospecify an absolute time of death for the message).

[0045] With respect to the hop count limit, this is initially set tosome value by the originating point and each time a message copy ispropagated, the hop count value in the message is decremented beforesending (conveniently, the hop count of a message can be decrementedimmediately the message is received by a device); if a receiving devicereceives a message with a zero hop count value (or, alternatively, ifthe hop count becomes zero when decremented by the device), it treatsthe message as no longer alive for the purposes of propagation. It wouldalso be possible to start with a zero count and increment it at eachhop, the message copy being treated as inactive when the count reaches aspecific value set by the device.

[0046] Setting a locale limit requires that the devices can find outtheir current position. This they may be able to do via some locationdiscovery means (GPS system; location server of mobile radioinfrastructure) to which they have access, or via information receivedover their short-range communication means. This latter case could beimplemented by arranging for messages transmitted by originating pointsto include position data of the originating points, the receiving devicethen determining its position by considering the position data containedin a set of the messages most recently received by the device. Thus, themost prominent (that is, frequently occurring) originating-pointposition in the set could be taken as the device's position, it beingappreciated that taking the position data of the most recently receivedmessage as representing the position of the device is unsound wherethere are more than one originating points in the vicinity. The set ofmessages used is conveniently defined by a time window though it wouldalso be possible to use a set of the last N messages. Rather than takingthe position of the most prominent originating point for the device'sposition, a weighted average could be used to estimate an intermediateposition between originating points; for example, if 80% ofmessagesreceived came from a first originating point and 20% from a secondoriginating point, the X coordinates of these two points could becombined in an 80:20 weighting ratio to give the X coordinate of thereceiving device with a similar calculation being effected to for the Ycoordinate.

[0047] The foregoing method of determining position by looking atposition data in a set of most recently received messages can, ofcourse, be employed independently of using the position information forrestricting propagation—for example, the position of the devicedetermined in this way can be used as input to a location aware serviceor simply presented to the device user.

[0048] In fact, it is possible to generate a boundary beyond which amessage is not to be propagated, without the need to include specificlocale limit data in the message. This involves detecting when thepercentage of messages coming from the same originating point as themessage under consideration has fallen below a threshold percentage thateffectively defines a “boundary” to the zone of influence of theoriginating point—if the current percentage is below the threshold, themessage of interest is not propagate. This mechanism is described inmore detailed below with reference to FIG. 7.

[0049] Device-set propagation limits—the involvement of each device inmessage propagation can be constrained by one or more of the following:

[0050] discarding without propagation subsequently received copies of amessage previously received;

[0051] limiting the number of times the device can transmit on themessage;

[0052] increasing the gap between re-transmissions of the message independence on how many times the message has been received by thedevice.

[0053] This latter restriction mechanism works on the basis that if alarge number of copies of a message are being received, then the devicecan reasonable infer that the message is circulating adequately withoutfurther copies being propagated at that time—in other words, theinter-sending gap should be increased. On the other hand, if nosubsequent copies are received, this can be interpreted as an indicationthat the user has moved to an area where none of the nearby devices haveany knowledge of the message, so the message should be repeated by thedevice somewhat more often, that is, the inter-sending gap should not beincreased. In the extreme, if more than a threshold number of copies ofa message are received, further propagation can be terminated (send gapset to infinity). Rather than adjusting the send gap simply independence on the total number of copies received of the same message,the send gap could be adjusted in dependence on the number of copiesreceived in a sliding time window or in dependence on some other measureof the current rate of receipt of message copies.

[0054] User Control—A more general form of propagation restriction canbe exercised by the user specifying the types of message in which theyhave an interest and only accepting messages of those types, messages ofother types being simply rejected without onward propagation. Thisfiltering of the messages handled and propagated by a device can beeffected according to at least one of:

[0055] the source of the message as indicated by a source identifiercontained in the message (if required, authentication mechanisms can beused to confirm the source identity);

[0056] the type of information contained in the message as indicated byan information-type data item in the message.

[0057] Of course, the user of a device, whilst still wishing to receivemessages, may not want his/her device to be used at all in messagepropagation and the device can be provided with means for enabling theuser to completely deactivate message propagation. However, this isprobably not desirable behaviour from the point of view of the partycontrolling the originating point as it interferes with the messagepropagation process whilst still benefiting the user. A way of requiringusers to either participate fully or not at all is to arrange for themessages only to be viewable, or otherwise presentable, to a user if themessage has been accepted for propagation. Since not all messageoriginators may want to require such a regime of operation and since thedevice will normally be intended to receive other types of messages (notjust those intended for propagation), it is convenient to append amessage class designator to each message, this message class designatoridentifying:

[0058] messages which must be accepted for onward propagation if themessage is to be accessible to the user of a device (such messages aretermed “propagation mandatory” or “PM” messages hereinafter)-;

[0059] messages the onward propagation of which is optional, themessages being accessible to the device user whether or not the messagesare accepted for propagation (such messages are termed “PropagationOptional” or “PO” messages hereinafter);

[0060] one or more other classes of message (for example, an “emergency”message class for messages, such as a fire alert, or a request for adoctor, that must be propagated under all circumstances).

[0061] The devices 10 are then arranged to recognise the class of amessage and operate accordingly. With respect to PO messages(propagation optional), the user determines by appropriate input totheir device whether or not such messages are to be propagated. Withrespect to PM messages (propagation mandatory), the devices preferablypermit a user to select whether to effect a general election of whetheror not to accept such messages for propagation, or to effect such anelection on a per message basis. In this later case, the user ispresented with an indicator of the contents/origin of a message beforemaking their election.

DEVICE EMBODIMENTS OF FIGS. 2 TO 6

[0062] Turning now to the particular embodiment of the mobile device 10shown in FIGS. 2 to 6, consideration is first given to the form ofinformation message 20 intended to be propagated through the device, itbeing understood that the illustrated message field structure (see FIG.2) is that of the message delivered by, and accepted by, the short-rangecommunications means of a device 10. Message 20 comprises the followingfields: Message class field 21 this field contains the class designatorindicating whether the message is of class PM, PO or other; Message IDfield 22 this field contains a unique identifier of a message, theidentified being retained by each copy of the same message; Messagesource ID this field contains the ID of the originating point field 2312 (fields 22 and 23 can be combined); Information type this fieldcontains an indication of the type of field 24 information carried bythe message - for example, whether it is advertising (and if so, whatgeneral type of product or service is involved) or position datarelating to the originating point; Information field 25 this fieldcontains the information being propagat- ed, - this will generally belocality information; Time-to-live field 26 this field contains thetime-to-live value discussed above in relation to limiting message life;Hop count field 27 this field contains the hop count discussed above inrelation to limiting message life - in this example, hop count isintended to be decremented to zero; Locale Limit field 28 this fieldcontains the locale limit information discussed above in relation tolimiting message propagation to a particular area.

[0063] As shown in FIG. 3, the mobile device 10 comprises receive andtransmit blocks 31 and 32 respectively that together form short-rangecommunication means (for example infra-red or radio based), a controlblock 40, a message store 41, and user interface 34 (typically, adisplay and input keypad) controlled by user interface control 42. Thecontrol block 40 controls the handling of messages received throughreceive block 31, passing them to store 41 and user interface 34 asappropriate and initiating their onward propagation through transmitblock 32 when required. The control block implements event handlerprocesses 46 and 47. Event handler 46 is operative to respond to amessage receipt event in respect of an PM (propagation mandatory)message as will be more fully described below; handler 46 also handlesPO (propagation optional) in the case that the device user 35 hasindicated that such messages are to be treated as PM messages (this userindication is input through interface and is stored in mode store 43).In addition to the PM message receipt handler 46, a second messagereceipt handler, not shown, is also provided for handling other messagesnot intended for propagation, including PO messages in the case that theuser has indicated that such messages are not to be propagated; thissecond message handler is not described herein as it does not form partof the present invention and can, in any case, be simply implemented topresent the received message to the user.

[0064] The event handler 47 services gap timeout events generated by agap timing block 45, the latter being tasked by control block 40 to timethe intervals between message resends. Handler 47 is responsible fordeciding whether following a timeout, the message concerned shouldactually be resent.

[0065] Mode store 43 as well as holding the user's choice in respect ofhow PO messages are to be handled, also stores user-set mode indicatorsas to whether PM messages are to be handled at all and, if so, whetherthey should be generically accepted for propagation or whether the usermust give his/her consent on a per message basis.

[0066] A store 44 holds the user's choice as to what type of informationare to be accepted and what sources are acceptable, this informationbeing used by event handler 46. Other elements of device 10 are alocation discovery block 33 (for example, a cellular radio unit by whichthe device may request its location from a location server of the mobilecellular radio infrastructure), and an audio alert device for alertingthe user to the receipt of a new message.

[0067] Each incoming message that is not immediately discarded is storedin a corresponding message entry 49 in message store 41. As well as themessage 20 itself, the message entry 49 holds the following items:Timestamp 91 this is the time of storage of the message in store 41; RXCount 92 this is the number of times copies of the same message havebeen received by the device; TX Count 93 this is the number of times themessage has been sent on; Dead Flag 94 this flag is set when the messageis no longer to be propagated, the message having become inactive forthis purpose, for example, as a result of a propagation limit havingbeen reached; Keep Flag 95 this flag is set in response to the userindicating that he/she wants the message to be kept; Delete Flag 96 thisflag is set when the user indicates no more interest in a message.

[0068] Message store is responsible for periodically running garbagecollection process 48 to remove message entries no longer requiredeither by the user or for onward propagation.

[0069] With respect to the PM message receipt handler 46, whenever amessage is received that has a class of PM (or PO if the user haselected to treat such messages as PM messages) then one of two thingshappens depending on whether or not the user has elected to reject allPM messages. If the user has elected to reject all PM messages, thehandler 46 is not called and the message is simply discarded; however,if the use has elected to receive PM messages, the handler is triggered46. Operation of handler 46 will now be described with reference to FIG.4.

[0070] Handler 46 first checks the message ID in message field 22 toascertain by comparison with the IDs of messages already held, whetherthe new message has already been received (see block 50)—if this is thecase, then the RX Count 92 for the copy of the message already stored isincremented and the gap time value currently being timed for the messageis increased (see block 51). If the just-received message has not beenreceived before, the message source and information type fields 23 and24 are checked (see block 52) against the user-specified acceptablevalues of these parameters held in store 44; if either or both fieldscontain unacceptable values, the message is discarded, otherwise it istime-stamped and stored in a new message entry 49 in store 41 and itshop count field 27 is decremented (see block 53). The flags 94 to 96 ofthe new message entry 49 are all initially in a reset state and the TXand RX counts are zero.

[0071] The user is now alerted, using alert device 36, to the receipt ofthe new message (see block 54).

[0072] What happens next depends on whether the user has genericallyelected that all PM messages (including PO messages treated as PMmessages) are accepted for propagation, or whether such election is tobe effected on a message-by-message basis (see block 55). In the formercase, processing continues at block 58 whereas in the latter case, theDead flag 94 for the message is “set” and the handler terminates itsoperation pending a message accept event which, if received, causesresetting of the Dead Flag (see block 57) before resuming processing atblock 58.

[0073] The operation of the device is such that it only permits a userto view a PM message if the message is accepted for propagation. Theinterruption of event-handler processing between blocks 56 and 57 is toascertain whether the user is willing to accept the message forpropagation so permitting it to be accessed by the user. Afterprocessing is discontinued at block 56, user interface control 42 causesindications about the message to be displayed (or otherwise presented tothe user) so as to enable the user to make an informed choice aboutwhether to accept the message. If the user elects to discard the messageby selecting delete from an option menu or if he user simply ignores themessage, it will in due course be removed from store 41 by the garbagecollection process 48 without having been made available for access bythe user and without having been propagated. On the other hand, if theuser accepts the message for propagation, the user is enabled to accessthe full message and the message is accepted for propagation—in thiscase, processing is resumed at block 47 as already indicated. Interfacecontrol 42 keeps track of whether a message has been accepted forpropagation, and is therefore to be fully accessible, by storing an IDlist of messages not yet accepted; alternatively, and extra flag inmessage entry 49 can be used for this purpose.

[0074] Where a user has elected generically to accept PM messages, thenno user intervention is required and the message is automaticallyaccepted for propagation and is accessible to the user; there is thus noneed to store an indication of which messages have yet to be accepted.

[0075] Continuing on the description ofthe operation of event handler 46at block 58, this and the following blocks are concerned with effectinga first onward propagation of the message. Whilst this initial sendingis not subject to a time-to-live check, both a hop count check (seeblock 58) and locale check (see block 59) are carried out. If bothchecks are passed, the message is sent on (see block 61) throughtransmit block 32; thereafter, TX Count 93 is incremented and gap timer45 is triggered to start timing an inter-sending gap the initialduration of which is preset. If either of the checks carried out inblocks 58 and 59 fails, the “Dead” Flag 94 is set (see block 60) and nofurther attempts are made to propagate the message.

[0076] With respect to the locale check carried out in block 59, thisinvolves comparing the locale specified in the location filed 28 withthe current device location as determined by the location discovery unit33. One way of implementing this comparison simply is to have the field28 include cellular radio cell IDs that are valid (that is, within whichthe message can be propagated) and arrange for the discovery unit (acellular radio device) 33 to extract current cell ID information fromsignals receive over the cellular network.

[0077] Considering next the gap timeout event handler 47 (see FIG. 5),when this handler is triggered by a sending-gap timeout generated byunit 45 in respect of a particular message, the handler 47 determineswhether it is appropriate to send out the message again. Moreparticularly, the handler first checks (see block 70) whether thecurrent duration of the holding time of the message in the device(current internal clock time less timestamp) is greater than thetime-to-live value held in message field 26. If this is the case, thenthe message has exceeded its lifespan and its associated Dead flag 94 isset (see block 76); no further propagation of the message is effected.However, if the message holding time is less than the time-to-livevalue, a location check is done (see block 71) in the manner alreadydescribed with respect to block 59. Again, if this check fails the Deadflag is set and no further sending is effected. However, if the locationcheck is passed, the message is re-sent but only after the value held inits time-to-live field 26 is reduced by the holding time of the messagein the device (this reduction is effected only for the sent copy of themessage, not the stored copy). Next, the TX Count for the message isincremented (see block 73) after which a check is made against apredetermined limit stored in device 10 (see block 74). If the TX Countvalue equals (or is greater than) the limit value, the message has beensent the maximum number of times permitted by the device and its Deadflag is set. If the limit has not yet been reached, the gap timer 45 istriggered again to start the timing of a new inter-sending gap for themessage. It may be noted that it is not whether the Dead Flag has beenset which controls whether or not a message is re-sent but, rather,whether the gap timer is re-triggered and, if so, whether the subsequentchecks carried out in blocks 70 and 71 are passed.

[0078] The purpose of the three flags Dead, Keep and Delete(respectively flags 94, 95 and 96) is to control whether or not amessage entry can be deleted form the store 41 by the garbage collectionprocess 48. In this respect, a user may decide he/she wishes to keep amessage (by using the user interface 34 to set the Keep flag 95)notwithstanding that the message is “dead” in relation to thepropagation process; however, a message that is not dead should not bedeleted. A complication also arises in that a message may dieimmediately after having been received and before the user has had arealistic chance to access it. All messages need to be given areasonable opportunity to be accessed by the user before removal; on theother hand, non-accessed messages cannot be stored for long periodsparticularly in areas where many different messages are being received.A compromise is to allow non-accessed messages that are dead to be heldfor up to ten minutes before removal from the store; if the userintervenes before the ten minutes has elapsed, then the Keep or Deleteflags will be set in which case these flags will determine whether ornot the dead message is removed.

[0079]FIG. 6 depicts the garbage collection process 48. First the DeadFlag of a message is checked (see block 80)—if this flag is not set themessage is retained. If the Dead flag is set, the Delete flag is nextchecked (see block 82)—if this flag is set the message entry is removed(see block 83). If the Delete flag is not set, the message holding timeis checked together with the status of the Keep flag (see block 82)—ifthe message has been held for more than ten minutes, then it is removedunless the Keep flag is set.

[0080] Rather than the fixed ten minute threshold discussed above, thisthreshold could be made adaptive according to the amount of free memoryspace in store 41.

[0081] Variants

[0082] Many variants are possible to the above-described embodimentofthe invention as will be appreciated by persons skilled in the art.

[0083]FIG. 7 illustrates one variant for judging location. Moreparticularly, FIG. 7A depicts the density of “live” or active messagesaround two originating points OP1 and OP2 respectively, as consideredover a time window (or a set of the N most recently received messages).The Figure shows separately the density variation for messages from eachof the two originating points (the density of live messages from OP1being highest at OP1 and then dropping away with distance, and themessages from OP2 exhibiting a similar density variation).

[0084] As would be expected, if a device moves from near OP1 towardsOP2, the device will receive an increasing number of messages from OP2.FIG. 7B depicts the percentage of messages being received by the devicefrom OP1 as the device is moved between OP1 and OP2.

[0085] By looking at this percentage, the device can decide whether itis “nearer” to OP1 than OP2, though this judgement will not necessarilycorrespond to one made on the basis of real physical distances. If thedevice is concerned to know its location and if originating-pointlocation information is contained in at least some of the messages fromeach originating point, the device which is receiving messagespropagated from both originating points can decide to which originatingpoint it is closest and therefore which originating-point location bestrepresents the device's own location. With more originating points, thetest as to which is the closest originating point becomes whichoriginating point is presenting the most messages to the device within aspecified time window.

[0086] The curve of FIG. 7B can also be used to determine a boundary tothe zone of influence of OP1 with this boundary then being used as alimit beyond which message propagation in respect of OP1 originatingmessages should cease in order to avoid excessive message diffusion. Inthe present example, the boundary is defined as where the receivedmessages coming from OP1 falls to 20% of the total received messages. Aboundary set in this manner has the advantage that it does not requirethe inclusion of locale limit data in each message.

[0087] Another variant concerns the method used to limit propagationbased on setting a limit to the message life. In the system and devicedescribed above, a message time-to-live value in message field 28 isdecremented as the message is propagated through the devices until thevalue reached zero—in effect, the message lifetime was specified by theoriginating point. An alternative is to use the field 28 as amessage-age field that is initially zero when the message is sent out bythe originating point but which is incremented by each propagatingdevice by an amount corresponding to the time the message spends in thedevice before being sent on. Each receiving device then decides whetherthe message has become too old to be worthy of sending on, the messageage being the value in field 28 of the received message plus the timespent by the message in the device before its intended propagation. Eachdevice can have a different message age threshold which can be user set.

[0088] Furthermore, in the above described embodiment, the receivingdevice checks immediately prior to the device's intended propagation ofthe message whether the message-life threshold has been exceeded; it isnecessary to wait to this moment because the sending gap is variable andtherefore a send time, and thus the remaining-life/age of the messagecannot be predicted in advance. However, in cases where the device isarranged to schedule message propagation in advance in a way thatenables it to know fairly accurately when the message is likely to besent, the device can at the same time check whether the message-lifethreshold of the message will have been exceeded at the time the messageis scheduled to be sent—if the threshold will have been exceeded thenthe message is not scheduled for sending.

[0089] Generally with respect to the defining parameters of the variouspropagation limiting techniques described above, the values of theseparameters can be made dependent on the message characteristics (messageclass/message source/information type); in this way, the propagation of,for example, advertising messages can be more restricted that that ofother message types.

[0090] As regards the application of user-specified message filters(step 52, FIG. 4), different filters can be applied to message viewingand message propagation. Also the time a message is retained in memoryfor propagation purposes can be made different from the time the samemessage is retained for the purposes of viewing purposes.

[0091] A useful behaviour, at least in some circumstances, is to arrangefor a device that is holding one or more messages for onwardtransmission, to send these messages immediately after having received amessage (or messages) from another device, there being a highprobability that the latter device will receive the transmittedmessages. The transmission of a message in this way will, of course,result in the updating of the message transmission count (indeed, thecount may be incremented by more than one to reflect the highprobability of message receipt).

1. A method of locally diffusing information for presentation to usersof mobile devices, the method involving propagating the information froman originating point in messages passed from device to device bynon-wired short-range communication means of the devices, the number ofcopies of a message in propagation initially tending to increase due tothe propagation activities of the receiving devices and then dying awayas the devices implement propagation limitation measures for themessage, at least one device being operative to send messages multipletimes with the interval between retransmissions ofthe message beingdependent on how many times the same message has been received by thedevice either in total or during a recent period.
 2. A method accordingto claim 1 , wherein the interval between retransmissions is increasedwith increasing number of receipts of the same message either in totalor during a recent period.
 3. A method according to claim 1 , whereineach message includes a message ID that serves to distinguish onemessage from another, the message ID enabling a receiving device toascertain if the same message has been previously received.
 4. A methodaccording to claim 1 , wherein if more than a predetermined number ofcopies of a message are received in total, said at least one devicesterminates further propagation of the message.
 5. A method according toclaim 1 , wherein if more than a predetermined number of copies of amessage are received during a recent period, said at least one devicesterminates further propagation of the message.
 6. A method according toclaim 1 , wherein the information comprises at least one of: informationwith at least an item that is explicitly or implicitly of localrelevance the position of the originating point.
 7. A mobile device forlocally diffusing information to other devices for presentation to theirusers, the mobile device comprising: a message store; a short-rangewireless transceiver for receiving messages and storing them to saidstore, and for transmitting messages retrieved from the store; a messagereceive/transmit counter for recording how many times each message isreceived and transmitted; and a message-propagation controller operativeto cause messages held in said store to be transmitted multiple timeswith the interval between retransmissions of each message beingdependent on how many times the same message has been received by thedevice, either in total or during a recent period, as indicated by saidcounter.
 8. A device according to claim 7 , wherein the controller isoperative to increase the interval between retransmissions of a messagewith increasing number of receipts of the same message either in totalor during a recent period.
 9. A device according to claim 7 , whereineach message includes a message ID that serves to distinguish onemessage from another, the message ID being used by said counter toascertain if the same message has been previously received.
 10. A deviceaccording to claim 7 , wherein if more than a predetermined number ofcopies of a message are received in total, the controller terminatesfurther propagation of the message.
 11. A device according to claim 7 ,wherein if more than a predetermined number of copies of a message arereceived during a recent period, the controller terminates furtherpropagation of the message.